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SJTU Team Released Dark-Exciton Phonon Connections on Nature Communications

July 22, 2019      Author:

Recently, the research team led by Prof. Ren Tianhui from the School of Chemistry and Chemical Engineering and Prof. Shi Sufei from Rensselaer Polytechnic Institute jointly published the paper Emerging Photoluminescence from the Dark-Exciton Phonon Replica in Monolayer WSe2 on the Nature Communications. The team found that a new type of quasi-particle (X_D^R) inherited the long lifetime of dark exciton and valley polarization of the bright exciton, which may lay a solid foundation for the development of quantum information processing and memory devices of the next generation.

Dr. Li Zhipeng, doctoral student Wang Tianmeng and Jin Chenhao are the first authors of the paper, and Prof. Ren Tianhui, Prof. Shi Sufei, and Dr. Cao Ting are the corresponding authors. Moreover, doctoral student Lu Zhengguang from FSU, Dr. Taniguchi and Dr. Watanabe from Japan, Prof. Tongay from Arizona State University, Prof. Li Yang from Washington University in St. Louis, and Dr. Smirnov from National High Magnetic Field Lab also contributed to the paper.

Abstract: Tungsten-based monolayer transition metal dichalcogenides host a long-lived “dark” exciton, an electron-hole pair in a spin-triplet configuration. The long lifetime and unique spin properties of the dark exciton provide exciting opportunities to explore light-matter interactions beyond electric dipole transitions. Here we demonstrate that the coupling of the dark exciton and an optically silent chiral phonon enables the intrinsic photoluminescence of the dark-exciton replica in monolayer WSe2. Gate and magnetic-field dependent PL measurements unveil a circularly-polarized replica peak located below the dark exciton by 21.6 meV, equal to E″ phonon energy from Se vibrations. First-principles calculations show that the exciton-phonon interaction selectively couples the spin-forbidden dark exciton to the intravalley spin-allowed bright exciton, permitting the simultaneous emission of a chiral phonon and a circularly-polarized photon. Our discovery and understanding of the phonon replica reveals a chirality dictated emission channel of the phonons and photons, unveiling a new route of manipulating valley-spin.

Translated by Huang Yiqing Reviewed by Wang Bingyu